Lightning Beast - Ornithopod dinosaur

Introduction

Fulgurotherium australe was a small ornithopod dinosaur from the Early Cretaceous of Australia. Fulgurotherium, known from Lightning Ridge in New South Wales and perhaps from Victoria, was one of the first Australian dinosaurs to be scientifically described. Lightning Ridge was on or near the palaeo-Antarctic Circle during the Early Cretaceous, and Fulgurotherium would have been adapted to survive in this extreme environment. The status of Fulgurotherium is uncertain both because of its fragmentary nature and because the relationships of all Australian ornithopods are poorly understood.

Identification

The original description of Fulgurotherium australe was based on the distal end of a fragmentary femur (upper leg bone) first identified as that of a small theropod (Huene 1932). Fulgurotherium is now recognized as a small ornithopod rather than a theropod, although its affinities are still uncertain (see below).

A study of additional Lightning Ridge ornithopod material by Molnar and Galton (1986) identified several more femora that might be from Fulgurotherium, presenting a ‘composite femur’ built from these incomplete specimens. Based on this composite, the femur of Fulgurotherium resembles that of ‘hypsilophodontids’, small ornithopods from the Jurassic and Cretaceous (reconstructions of Fulgurotherium have been based on Hypsilophodon foxii from the Early Cretaceous of Europe). The shaft of the femur is curved distally, the thin, sheet-like lateral condyle of the femur is narrow and smaller than the medial condyle, the rod-like lesser trochanter is lower than the greater trochanter, greater and lesser trochanters are separated by a shallow cleft (or no cleft at all), and there is a very shallow intercondylar groove distally.

Other isolated postcranial bones and teeth from Lightning Ridge are tentatively referred to Fulgurotherium although no skull, lower jaw or other associated fossils have been found. Several femora from the Early Cretaceous of Victoria are also referred to Fulgurotherium although this collection seems to be a somewhat mixed bag of various femora, not all of which resemble that of Fulgurotherium (the authors of that study, Pat and Tom Rich of Victoria, suggest the material could alternatively represent at least three new ornithopod genera).

Fulgurotherium at present can only be diagnosed from femoral characters, since no other fossils can be positively attributed to this species. Such problems highlight the difficulties faced when species are named on isolated remains. Fulgurotherium, fragmentary and not found as even a partial articulated skeleton, may not yet be adequate for the diagnosis of a distinct genus and species. Fulgurotherium may therefore become nomen dubium (a species of doubtful taxonomic validity) until (andif) more complete fossil material is found.

Habitat

Lightning Ridge during the Early Cretaceous was close to the palaeo-Antarctic Circle. This southern high-latitude position meant the area experienced extremes of daylight during winter and summer months, although the climate was much milder then than it is today. The now-dry Lightning Ridge area was then forested and close to the Eromanga Sea, an inland sea that covered vast areas of central Australia during the Cretaceous.

Preserved tree branches, twigs and conifer cones suggest that the Lightning Ridge flora was fairly typical of Early Cretaceous Australia. Araucarian conifers and ginkgoes were probably the dominant forest trees. The understorey would have been comprised of ferns and cycads, and reeds and horsetails would have grown by the numerous waterways. The diverse fauna of Lightning Ridge included abundant molluscs, freshwater crustaceans, freshwater fish (bony fish and lungfish), turtles, crocodiles, dinosaurs (theropods, sauropods and ornithischians), pterosaurs, plesiosaurs, mammals and possibly birds.

Southern Victoria during the Early Cretaceous lay south of the palaeo-Antarctic Circle and would have experienced even greater extremes of daylight than Lightning Ridge. Evidence for rafting ice on the Eromanga Sea and studies of cryoturbation structures from the area (deformations in sediments caused by the seasonal freezing and thawing of soils) suggest that the climate may have at times been quite cold, with winter ice and seasonally frozen ground. Evergreen araucarian conifers and podocarps and deciduous ginkgoes would have been important forest trees. The understorey would have included pentoxylaeans, ferns, bryophytes and mosses, and horsetails and reeds would have lined the streambanks. In Victoria, Fulgurotherium shared its habitat with other dinosaurs, fish (including lungfish), ancient labyrinthodont amphibians, pterosaurs, crocodyliforms and early Australian mammals (monotremes, ausktribosphenids and multituberculates).

Distribution

Fulgurotherium australe was described from Lightning Ridge, New South Wales. Additional fossils referred to Fulgurotherium were found at Flat Rocks and Dinosaur Cove in Victoria, although these identifications are problematic.

Feeding and diet

Fulgurotherium, like most ornithopods, would almost certainly have been a plant-eater. Edible plants known from the Early Cretaceous of eastern Australia include ferns, horsetails and other low-growing Cretaceous plants.

Other behaviours and adaptations

Small ornithopods were remarkably common in Cretaceous Australia, particularly in southern Victoria, and may have travelled in small herds or flocks. Dinosaur burrows, possibly those of small ornithopods, were recently discovered in Victoria. Perhaps Fulgurotherium and other small ornithopods spent the coldest months of the year underground.

Fossils description

The original specimen (holotype) of Fulgurotherium is the distal end of a fragmentary, opalised femur. Other referred fossils from Lightning Ridge include a partial scapula, six additional femora (a seventh femur may represent a second ornithopod species), and a single tooth of the right size to be that of Fulgurotherium (from Molnar and Galton 1986). Small ornithopod fossil material from Victoria (from both the Otway and Strzelecki Groups, Flat Rocks and Dinosaur Cove respectively) includes incomplete skulls and a partial skeleton, some of which may also be Fulgurotherium (Molnar 1991). Additional femora from Victoria have also been tentatively assigned to Fulgurotherium, but these vary in size and form and may represent at least three new genera (Rich and Vickers-Rich 1989).

The holotype of Fulgurotherium is held by the Natural History Museum in London (BMNH R.3719) and there is a cast of the original at the Australian Museum.

Evolutionary relationships

Fulgurotherium was long thought to be a hypsilophodontid, along with Leaellynasaura amicagraphica and Qantassaurus intrepidus. However, ‘Hypsilophodontidae’ is probably a grade of small ornithopods rather than a natural group, with at least some ‘hypsilophodontids’ (like Fulgurotherium, Leaellynasaura and Qantassaurus) now considered to be basal ornithopods of uncertain affinities (Euornithopoda incertae sedis: Norman et al. 2004). Relationships of basal ornithopods are currently unresolved, and much more work is needed on the interrelationships of ornithopod dinosaurs in general.

The status of Fulgurotherium, Leaellynasaura, Qantassaurus and Atlascopcosaurus is currently under review. Some researchers believe additional fossil material should not be referred to any of these taxa (for instance, Butler et al. 2008). Fulgurotherium is treated here as a valid species until its affinities are reviewed.

References

• Butler, R. J., Upchurch, P. and Norman, D. B., 2008. The phylogeny of the ornithischian dinosaurs. Journal of Systematic Palaeontology 6(1), 1-40.
• Huene, F. von, 1932. Die fossile Reptil-Ordnung Saurischia, ihre Entwicklung und Geschichte. Monograph Geol. Palaeontol. (series 1) 4, 1-361.
• Molnar, R. E., 1991. Chapter 18: Fossil Reptiles in Australia. Pp. 605-701 in Vickers-Rich, P., Monaghan, J. M., Baird, R. F. and Rich, T. H. (eds) Vertebrate Palaeontology of Australasia. Pioneer Design Studio, Lilydale, Victoria.
• Molnar, R. E. and Galton, P. M., 1986. Hypsilophodontid dinosaurs from Lightning Ridge, New South Wales, Australia. Geobios 19, 231-239.
• Norman, D. B., Sues, H.-D., Witmer, L. M. and Coria, R. A., 2004. Basal Ornithopoda. Chapter 18 in Weishampel, D. B., Dodson, P. and Osmólska, H. (eds) The Dinosauria (Second Edition). University of California Press, Berkeley.
• Scanlon, J. D., 2006. Chapter 15: Dinosaurs and other Mesozoic reptiles of Australasia. Pp. 265-290 in Merrick, J. R., Archer, M., Hickey, G. M. and Lee, M. S. Y. (eds) Evolution and Biogeography of Australasian Vertebrates. Australian Scientific Publishing, Oatlands.
• Rich, T. H. V. and Rich, P. V., 1989. Polar dinosaurs and biotas of the Early Cretaceous of southeastern Australia. National Geographic Research 5, 15-53.
• Rich, T. H. and Vickers-Rich, P., 1999. The Hypsilophodontidae from southeastern Australia. Pp. 167-180 in Tomida, Y., Rich, T. H. and Vickers-Rich (eds) Proceedings of the Second Symposium on Gondwanan Dinosaurs. National Science Museum of Japan, Tokyo.
• Rich, T. H., Vickers-Rich, P. and Gangloff, R. A., 2002. Polar dinosaurs. Science295, no. 5557, 979-980.

Further reading

• Flannery, T. F. and Rich, T. H., 1981. Dinosaur digging in Victoria. Australian Natural History 20, 195-198.
• Long, J. A., 2002. Dinosaurs of Australia and New Zealand and Other Animals of the Mesozoic Era. New South Wales University Press, Sydney.
• K. Carpenter (ed) 2006. Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs.Indiana University Press, Bloomington.
• Rich, T. H. and Vickers-Rich, P. 2000. Dinosaurs of Darkness. Indiana University Press, Bloomington.
• Ritchie, A. 1987. Precious relics from Lightning Ridge: Fulgurotherium australe. Pp. 42-44 in Hand, S. and Archer, M. (eds) The Antipodean Ark. Angus and Robertson, North Ryde. Illustrations by Peter Schouten.